1. Field of the Invention
The present invention relates to a thin-film heat sink made of a thin film and a method of manufacturing the same.
2. Description of the Related Art
A heat sink is used to radiate heat generated from electronic components rapidly and to cool elements. Typical materials used for heat sinks include diamond, silicon carbide (SiC) and aluminum nitride (AlN). Bulk AlN has thermal conductivity of 170 W/mK or more, which is eight to ten times higher than that of aluminum oxide (Al2O3).
For thin-film magnetic heads, especially those incorporating giant magneto-resistive (GMR) elements that exhibit GMR effect, consideration is being given to the use of thin-film heat sinks, formed of materials having high thermal conductivity, as various insulating films in the heads in order to reduce noise arising from heat generated from read elements.
For making the thin-film heat sinks for the above-mentioned heads, it is preferred to use films that can be formed at relatively low temperatures (substrate temperature within a range from room temperature to 200xc2x0 C.), so as to prevent destruction of read elements by heat generated when the thin-film heat sinks are formed.
To form films with a structure providing good thermal conductivity, a substrate temperature required for diamond is 600 to 800xc2x0 C. and that for SiC is 300 to 600xc2x0 C. On the other hand, a substrate temperature required for AlN ranges from room temperature to 200xc2x0 C. In view of this, it has been proposed to use AlN films instead of conventional Al2O3 films for various insulating films in the thin-film magnetic heads to reduce noise arising from heat generated from read elements.
However, AlN films have a compressive stress as high as 108 to 109 Pa, which is about ten times that for Al2O3 films formed by sputtering. The compressive stress causes two problems: deterioration in adhesiveness of the AlN film to a base, and generation of noise arising from the stress.
As a solution to the problem of deterioration in adhesiveness of AlN films to a base, a method has been proposed, in which an Al2O3 film is formed on a base by conventional sputtering method and an AlN film is formed thereon to improve the adhesiveness of the AlN film, as disclosed in Published Unexamined Japanese Patent Application (KOKAI) Heisei 11-154310 (1999), for example.
This method has an effect of making the AlN film adhere to the base via the Al2O3 film. However, it does not reduce the internal stress of the AlN film. It means that this method cannot reduce noise generated in read signals when, for example, a thin-film heat sink including an AlN film is provided near a GMR element.
To implement a thin-film heat sink with a sufficient property as a heat sink, it is desirable that the thin-film heat sink has a thickness of 100 nm or more. However, since the internal stress of a thin-film heat sink increases with an increase in its thickness, the problem resulting from the internal stress becomes more remarkable as the thickness of the thin-film heat sink is made greater.
It is an object of the invention to provide a thin-film heat sink with high thermal conductivity, high adhesiveness to a base and low internal stress, and to a method of manufacturing such a thin-film heat sink.
A thin-film heat sink of the invention comprises: a heat sink film functioning as a heat sink; and a bonding film for bonding the heat sink film to a base, wherein: one of the heat sink film and the bonding film is a film of which internal stress is compressive stress, and the other is a film of which internal stress is tensile stress.
According to the thin-film heat sink of the invention, the heat sink film having high thermal conductivity is bonded to the base via the bonding film. It is therefore possible to enhance adhesiveness of the thin-film heat sink to the base while attaining high thermal conductivity of the thin-film heat sink. Furthermore, according to the invention, the heat sink film and the bonding film have internal stresses in opposite directions. It is therefore possible to reduce the internal stress of the thin-film heat sink as a whole.
In the thin-film heat sink of the invention, the heat sink film may be a film of which internal stress is compressive stress, while the bonding film may be a film of which internal stress is tensile stress.
In the thin-film heat sink of the invention, the heat sink film may be an aluminum nitride (AlN) film.
In the thin-film heat sink of the invention, the bonding film may be an aluminum oxide (Al2O3) film formed through chemical vapor deposition.
In the thin-film heat sink of the invention, the bonding film may be a nitrogen-excessive silicon nitride (SiNx, where x is larger than one) film.
The thin-film heat sink of the invention may have a structure in which a plurality of heat sink films and a plurality of bonding films are alternately stacked.
In the thin-film heat sink of the invention, the heat sink film may have thermal conductivity of 0.8 W/mK or higher as thin film.
The thin-film heat sink of the invention may be used as an insulating layer of a thin-film magnetic head.
A method of the invention is provided for manufacturing a thin-film heat sink comprising a heat sink film functioning as a heat sink, and a bonding film for bonding the heat sink film to a base. The method includes the steps of: forming the bonding film on the base; and forming the heat sink film on the bonding film, wherein: one of the heat sink film and the bonding film is a film of which internal stress is compressive stress, and the other is a film of which internal stress is tensile stress.
According to the method of manufacturing a thin-film heat sink of the invention, the heat sink film having high thermal conductivity is bonded to the base via the bonding film. It is therefore possible to enhance adhesiveness of the thin-film heat sink to the base while attaining high thermal conductivity of the thin-film heat sink. Furthermore, according to the invention, the heat sink film and the bonding film have internal stresses in opposite directions. It is therefore possible to reduce the internal stress of the thin-film heat sink as a whole.
In the method of manufacturing a thin-film heat sink of the invention, the heat sink film may be a film of which internal stress is compressive stress, while the bonding film may be a film of which internal stress is tensile stress.
In the method of manufacturing a thin-film heat sink of the invention, the heat sink film may be formed of an aluminum nitride (AlN) film.
In the method of manufacturing a thin-film heat sink of the invention, an aluminum oxide (Al2O3) film as the bonding film may be formed through chemical vapor deposition in the step of forming the bonding film.
In the method of manufacturing a thin-film heat sink of the invention, the bonding film may be formed of a nitrogen-excessive silicon nitride (SiNx, where x is larger than one) film.
In the method of manufacturing a thin-film heat sink of the invention, the step of forming the bonding film and the step of forming the heat sink film may be alternately performed a plurality of times to make a thin-film heat sink having a structure in which a plurality of heat sink films and a plurality of bonding films are alternately stacked.
In the method of manufacturing a thin-film heat sink of the invention, the heat sink film may have thermal conductivity of 0.8 W/mK or higher as thin film.
The method of manufacturing a thin-film heat sink of the invention may manufacture a thin-film heat sink used as an insulating layer of a thin-film magnetic head.
Other and further objects, features and advantages of the invention will appear more fully from the following description.